1. Field of the Invention
This invention relates to a rotary dobby for the operation of the heddle frames installed on a loom and a weaving loom and to a loom provided with such a dobby.
2. Description of the Related Art
It is known that in rotary dobbies the vertical movement of the heddle frames is provided by oscillating components that can be constituted, depending on the case, by connecting rod-arm assemblies or by roller-bearing arms; these oscillating parts are driven by actuating elements in the form of an eccentric gear in the first case or of a cam in the second one. These actuating elements are mounted on a main shaft of the mechanism that is actuated by an intermittent rotary movement and, at the time of each stoppage, as a matter of fact at all the half turns of the above-mentioned shaft, the reading-in device must interlock the actuating element either with the shaft, in order to drive the oscillating part, or with a stationary point in order to effect the angular immobilization of the latter; this interlocking must be effected at each of the heddles of the dobby, that is to say of the actuating unit associated with each heddle frame and depending on the design or pattern to be obtained on the loom during the weaving process.
This selective interlocking is generally obtained by means of a cotter or catch-shaped movable coupling element subjected to the action of two pivoting arms arranged on one and the other sides of the shaft in order to actuate this moveable element at its two stop positions, being each pair of pivoting arms controlled by the reading-in device of the dobby.
In patent application FR-A-2 540 524 was disclosed a rotary dobby for looms in which a plate joined to each heddle frame is comprised of two diametrically opposed notches suitable to interact with the catch of two pivoting arms that are controlled by the reading-in device. These two notches are of different shape because one of them must be relatively deep in order to provide the plate with a perfectly precise angular position and then ensure an adequate holding for as long as necessary. On the other hand, the other notch is of reduced depth and is provided with lateral walls which are wide open and that run parallel to the chamfers of the extremities of the sides of the catch of each pivoting arm, so that the arm's catch can be automatically driven with the rotation of the plate, without the actuating of the reading-in device upon the arm. In this second case, one talks about a "passive" engaging of the catch in the notch.
Tests have shown that such an arrangement functions in a satisfactory manner. In this known device, however, when, depending on the pattern of the loom that is being woven, it is not necessary to exert on the coupling pawl a force causing it to actuate, the tappet of the reading-in device must be deflected towards the arm of which the catch is in passive engagement with the notch of the plate diametrically opposed to it, which allows the actuating of the pawl. Thus, in approximately 50% of the cases, the arm that is in a passive engagement with one of the notches of the plate is actuated although this is not necessary for a good operation of the dobby of the invention.
An excessive energy consumption of the dobby, a high noise level and repeated mechanical stresses on the components of the dobby are elements that are certainly not beneficial for the functioning of the mechanism. In view of these repeated stresses, the dimensioning of the drive shafts, of the flanges and of the reading-in device's tappet gave rise to their high cost and considerable size.